Neither. Actually, pineapples are a type of bromeliad. Easily grown at home, just cut off the tops and put in a glass of water until it grows roots, then pop 'em in the ground (or a pot, in colder areas).
Well, I don't have kids myself, so I'm never really sure how to answer their questions...
But I do remember my mom explaining it to me, when I was little, and I asked. She told me it was the darndest thing she'd ever seen, driving by a pineapple plantation. Told me how there were these low growing, spiky plants, and the little pineapple fruits just sitting on top of 'em like little hats.
Maybe: They grow on plants that look like the tops, but bigger. And the top IS a baby plant, that can grow big, and after a whole year, grows a stem up out of the middle, with a pineapple fruit, with a baby plant on top of that.
And endless daisy chain, going back in Time. A philosophical concept that amuses me... Go ahead, confuse the children!